man pppoectl ..
SYNOPSIS
     ispppcontrol [-v] ifname [parameter[=value]] [...]
     pppoectl -e ethernet-ifname [-s service-name] [-a
              access-concentrator-name] ifname
#!/bin/sh 
# Need ethernet interface UP (or it won't send any packets) 
ifconfig rtk0 up mtu 1500
 
# Create a pseudo device 
ifconfig pppoe0 create # Let pppoe0 use rtk0 as it's ethernet interface 
pppoectl -e rtk0 pppoe0 
 
# Configure authentication 
pppoectl pppoe0 \ 
       myauthproto=pap \ 
       myauthname=???? \ 
       myauthsecret=???? \ 
       hisauthproto=none 
 
# Configure the pppoe0 interface itself. This addresses are magic 
# meaning we don't care about either address and let the remote 
# ppp choose them. 
ifconfig pppoe0 0.0.0.0 0.0.0.1 up mtu 1454
 
route flush 
route add -net default 0.0.0.1 -iface